1. Field of the Invention
The present invention relates to a dual spin valve sensor with a self-pinned layer and a specular reflector and, more particularly, to a read head that produces a double spin valve effect with a pinned layer structure and self-pinned layer wherein the pinned layer structure is pinned by a pinning layer and the self-pinned layer is pinned by sense current fields and interfaces a specular reflector layer for reflecting conduction electrons into the mean free path of conduction electrons.
2. Description of the Related Art
An exemplary high performance read head employs a spin valve sensor for sensing magnetic fields on a moving magnetic medium, such as a rotating magnetic disk or a linearly moving magnetic tape. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90xc2x0 to an air bearing surface (ABS) which is an exposed surface of the sensor that faces the magnetic medium. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetic moment of the free layer is free to rotate in positive and negative directions from a quiescent or zero bias point position in response to positive and negative magnetic signal fields from a moving magnetic medium. The quiescent position is the position of the magnetic moment of the free layer when the sense current is conducted through the sensor without magnetic field signals from a rotating magnetic disk. The quiescent position of the magnetic moment of the free layer is preferably parallel to the ABS. If the quiescent position of the magnetic moment is not parallel to the ABS the positive and negative responses of the free layer will not be equal which results in read signal asymmetry.
The thickness of the spacer layer is chosen to be less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces or boundaries of the spacer layer with the pinned and free layers. When the magnetic moments of the pinned and free layers are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. An increase in scattering of conduction electrons increases the resistance of the spin valve sensor and a decrease in scattering of the conduction electrons decreases the resistance of the spin valve sensor. Changes in resistance of the spin valve sensor is a function of cos xcex8, where xcex8 is the angle between the magnetic moments of the pinned and free layers. This resistance, which changes when there are changes in scattering of conduction electrons, is referred to in the art as magnetoresistance (MR). Magnetoresistive coeffecient is dr/R where dr is the change in magnetoresistance of the spin valve sensor from minimum magnetoresistance (magnetic moments of free and pinned layers parallel) and R is the resistance of the spin valve sensor at minimum magnetoresistance. For this reason a spin valve sensor is sometimes referred to as a giant magnetoresistive (GMR) sensor. A spin valve sensor has a significantly higher magnetoresistive (MR) coefficient than an anisotropic magnetoresistive (AMR) sensor which does not employ a pinned layer.
The spin valve sensor is located between first and second nonmagnetic nonconductive first and second read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. The distance between the first and second shield layers is referred to in the art as the read gap. The read gap determines the linear bit density of the read head. When a magnetic disk of a magnetic disk drive rotates adjacent the read sensor, the read sensor detects magnetic field signals from the magnetic disk only within the read gap, namely the distance between the first and second shield layers. There is a strong-felt need to decrease the read gap so that the sensor is capable of detecting an increased number of field signals along a track of the rotating magnetic disk. By decreasing the read gap the magnetic storage capability of the disk drive is increased. These kinds of efforts have improved the magnetic storage of computers from kilobytes to megabytes to gigabytes.
Another scheme for increasing the magnetic storage of a disk drive in a computer is to provide a read sensor that produces a dual spin valve effect. This is accomplished by providing a ferromagnetic free layer structure between nonmagnetic conductive first and second spacer layers with the first and second spacer layers are located between first and second ferromagnetic pinned layer structures. The first pinned layer structure is exchange coupled to a first antiferromagnetic pinning layer which pins a magnetic moment of the first pinned layer structure in a first direction, typically perpendicular to the ABS, either toward or away from the ABS, and the second pinned layer structure is exchange coupled to a second antiferromagnetic pinning layer which pins the magnetic moment of the second pinned layer structure in the same direction as the moment of the first pinned layer structure. This scheme sets the magnetic moments of the first and second pinned layer structures in phase with respect to one another. The free layer structure has a magnetic moment which is typically parallel to the ABS, so that when magnetic field signals from a rotating magnetic disk are sensed by the read sensor the magnetic moments of the free layers rotate upwardly or downwardly, producing an increase or decrease in the aforementioned magnetoresistance, which is detected as playback signals. The importance of the dual spin valve sensor is that the spin valve effect is additive on each side of the free layer between the free layer structure and the first and second pinned layer structures. Unfortunately, the dual spin valve sensor is significantly thicker than a single pinned spin valve sensor because of the thicknesses of the first and second pinning layers. While the thicknesses of the various layers of a typical spin valve sensor range between 10 xc3x85-70 xc3x85 the thicknesses of the antiferromagnetic pinning layers vary in a range from 120 xc3x85-425 xc3x85. Iridium manganese (IrMn) permits the thinnest antiferromagnetic pinning layer of about 120 xc3x85 whereas an antiferromagnetic pinning layer composed of nickel oxide (NiO) is typically 425 xc3x85. There is a strong-felt need to provide a dual GMR or spin valve sensor which is thinner than prior art dual spin valve sensors so that a dual spin valve effect can be obtained without significantly increasing the read gap.
The present invention provides a novel dual spin valve sensor which is thinner than prior art dual spin valve sensors. The present dual spin valve sensor may be the same as the aforementioned dual spin valve sensor except one of the pinned layer structures is a self-pinned layer which is located between a specular reflector structure and one of the spacer layers. The magnetic moment of the self-pinned layer is not pinned by an antiferromagnetic pinning layer but, in contrast, the magnetic moment is pinned by sense current fields from other layers in the spin valve sensor when the sense current is conducted through the spin valve sensor. In order for this to occur the thickness of the self-pinned layer should be maintained below 15 xc3x85 with a preferable thickness of 10 xc3x85. The reason for this is because the thicker the self-pinned layer the greater the sense current fields that are required to pin the magnetic moment of the self-pinned layer. Unfortunately, when the self-pinned layer is thin there is a scattering of conduction electrons at a boundary of the self-pinned layer, which reduces the number of conduction electrons in the mean free path which, in turn, reduces the magnetoresistive coefficient (dr/R). The ideal situation is for the scattering events of the conduction electrons in the mean free path to be in phase. When there is scattering at a boundary of the mean free path this is referred to in the art as inelastic scattering which causes the scattering events to be out of phase and to work against one another to reduce the magnetoresistive coefficient (dr/R). Accordingly, a thin self-pinned layer does not provide an adequate boundary for the mean free path to prevent boundary scattering of conduction electrons.
I have found that by locating the self-pinned layer between a specular reflector structure and one of the spacer layers that the scattering of the conduction electrons at the boundary can be obviated. In a preferred embodiment, the specular reflector structure includes a first specular reflector layer composed of silver (Ag) and a second specular reflector layer composed of copper (Cu) with the second specular reflector layer being located between and interfacing the first specular reflector layer and the self-pinned layer. The specular reflector structure functions as a mirror in that conduction electrons are reflected by the specular reflector structure back into the mean free path of conduction electrons. Silver (Ag) is a better specular reflector than copper (Cu). Accordingly, the first specular reflector layer of silver (Ag) reflects the majority of the conduction electrons while the second specular reflector layer (Cu) reflects a smaller portion of the conduction electrons. However, the second specular reflector layer of copper (Cu) is highly desirable because of its compatibility with materials employed for the self-pinned layer and particularly for promoting a uniform microstructure of the self-pinned layer which increases the magnetoresistive coefficient (dr/R).
In a preferred embodiment I have maintained the thickness of the second reflector layer of copper (Cu) as thin as possible so as to reduce current shunting. Current shunting is a portion of the sense current which is conducted through layers other than the free layer structure and the first and second spacer layers. Current shunting also reduces the magnetoresistive coefficient (dr/R). Accordingly, the second specular reflector layer of copper (Cu) is maintained with a thickness of about 10 xc3x85. In the preferred embodiment the thickness of the first specular reflector layer of silver (Ag) is 20 xc3x85. Accordingly, a total thickness of 30 xc3x85 of the specular reflector structure is significantly less than the thickness required for an antiferromagnetic pinning layer. In this example, the overall thickness of the present dual spin valve sensor is reduced by the difference between the thickness of an antiferromagnetic pinning layer and 30 xc3x85. This can result in the present dual spin valve sensor having its thickness reduced by 90 xc3x85-395 xc3x85.
An object of the present invention is to provide a dual spin valve read sensor which has a reduced thickness.
Another object is to provide a dual spin valve read sensor which has only one antiferromagnetic pinning layer.
A further object is to provide a dual spin valve sensor which has a specular reflector structure next to a self-pinned layer for reflecting conduction electrons into a mean free path of conduction electrons for increasing the magnetoresistive coefficient (dr/R).
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.